This invention relates to finely porous clay formed preponderantly of a smectite type mineral and having crystal layers separated by intervals of not less than 22 .ANG. and to a method for the manufacture of the clay.
The category of smectite type minerals includes montmorillonite, bentonite, chlorite, beidellite, and synthetic mica. In the crystalline structure of montmorillonite, for example, a layer of silica tetrahydrons, a layer of alumina octahydrons, and a layer of silica tetrahydrons are bound in a superposed manner to form one crystal layer. The aluminum which constitutes itself the central metal of the layer of octahedrons is partly substituted by magnesium, a substance having a smaller positive charge than aluminum. The crystal layer, therefore, assumes a negative charge. An alkali metal ion (mainly Na.sup.+) corresponding to this negative charge intervenes between the crystal layers to keep the electric charge of the crystal layer neutral. Montmorillonite, therefore, possesses abundant cation-exchange ability. Further, chiefly owing to the hydrating property of this exchanging cation, this ore absorbs a significant volume of water between the crystal layers and manifests a strikingly high swelling property. The other smectite type minerals possess properties similar to such properties of montmorillonite.
Attempts are being made to use these smectite type minerals as catalyst carriers, heat insulators, or adsorbents by making the most of their multilayer crystalline structures.
When a smectite type mineral is mixed with water, water enters the intervals between the crystal layers. The intervals between the crystal layers vary in size with the mixing ratio of the ore with water. In the presence of ample supply of water, these intervals can increase to the maximum of about 500 .ANG.. When the smectite type mineral is mixed with water containing a cation such as Al.sup.3+ or Ca.sup.2+, the positive charge between the crystal layers is heightened and the intervals between the crystal layers are decreased. As the amount of the cation continues to increase, the intervals decrease eventually to about 10 .ANG..
Japanese Patent Disclosures SHO 54(1979)-5884 and SHO 54(1979)-16386 disclose inventions relating to a method for the manufacture of a porous clay of smectite type mineral containing between the layers of the smectite type mineral a cationic hydroxy metal complex, aluminum chlorohydroxide complex, silicates, phosphates, and zirconia by mixing the smectite type mineral, a cationic inorganic substance, and water, causing the cationic inorganic substance to exchange ion with the exchanging cation between the crystal layers, and hydrolyzing the resultant composite. In this porous clay, the intervals between the crystal layers are not more than about 10 .ANG..
If a smectite type mineral clay having such small intervals between the crystal layers is used as an adsorbent or a heat insulator, there are times when the clay will not bring about the intended effect as much as desired. When this clay is used for refining gasoline, for example, only low molecular hydrocarbons of smaller numbers of carbon atoms among other hydrocarbons of gasoline are allowed to enter the intervals between the crystal layers while hydrocarbons of relatively high molecular weights having larger numbers of carbon atoms are prevented from entering such intervals. Thus, the clay fails to manifest the intended effect sufficiently in refining the gasoline. If this clay is used as a heat insulator, the intervals between the crystal layers are filled to capacity with water simply on exposure to a mass of gas having a relative humidity of about 10%.
In the circumstance, there has been a strong demand for the development of finely divided porous clay having crystal layers separated by much larger intervals and a method for the manufacture of the clay.
An object of this invention is to provide a smectite type mineral clay having larger intervals between crystal layers than the conventional smectite type mineral clay.
Another object of this invention is to provide a method for the manufacture of a smectite type mineral clay having larger intervals between crystal layers than the conventional smectite type mineral clay.